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Friday, August 24, 2007

The Marathon preview: The weather factor

The World Athletics Championships kicks off tomorrow, and the first event, as has become tradition, is the marathon, this time for men.

The Osaka Weather

Another tradition, for it seems to be topical every time there is a Championship marathon, is the weather. The Five-day forecast for Osaka will no doubt have been giving some of the athletes sleepless nights - peak temperatures hitting 35 degrees Celsius (that is 95 Fahrenheit!). This is even hotter than in Athens, where the temperature was a real factor in the outcome of the women's race in particular. As has become customary, the race will be run in the early morning (7am) start in Osaka (which makes it difficult for anyone on a European timezone!), giving the athletes some reprieve. But not that much - the night-time temperatures in Osaka over the next five days averages 26 degrees celsius (79 Fahrenheit), which is still substantially warmer than most of the big-city marathons will ever be run at. The temperature during this year's London Marathon, for example, was hotter than ever before, causing many athletes to struggle and even suggest that the race be cancelled. The temperature there? 25 degrees, at peak. In fact, this excerpt from a news article on the race illustrates just how severe Osaka will be compared to the 'difficult' London Marathon:

The thermometer climbed from 14.1° (with 55% humidity) at the start of the
women’s race to 16.3° (49% humidity) after an hour, 18.6° (43%) after two hours
… and 20.5° after three hours, when the later-starting men’s race was reaching
its testing phases.

So there is clearly no comparison between what the elite athletes face in Osaka and what they might have faced in London. But what can we expect from the physiology of the runners in these races, beginning with tomorrow's women's race?

When size does matter...

The first thing (and this is a dramatically summarized version) is that the winner has to be small in size. All things being equal (which we concede they never are!), the smaller athlete will win a race in the heat. Many studies have shown this, and the equations that we use to model performances in the heat suggest the same. Basically, it boils down to a balance between height production and heat loss. Heat production is dependent on body size and running speed, while heat loss is a function of body surface area, and the environment. Obviously, the environment is the same for everyone, but body size is not. The smaller the athlete, the less heat they produce, but their heat loss is not reduced by as much and the end result is that the smaller athlete will store less heat running at a certain speed than the bigger athlete. Ultimately, this means that a smaller athlete can afford to run slightly faster before their body temperature rises. Big advantage! This is of course a oversimplification, but it does illustrate the point that when the mercury starts climbing, the advantage lies with a smaller runner.

Doing time in the heat - acclimatization is vital

The next important factor is acclimatization. Numerous studies have shown just how much performance improves after a period of adaptation to the heat. The guru of exercise in the heat, Bodil Nielsen of Denmark, has done many of these studies, and has shown how exercise tolerance improves almost two-fold after a period of hot weather adaptation. That is, athletes can go twice as far in the heat on the 7th day compared to their first day in the heat. This means that a winning athlete is one who is well adapted to running in the heat. The advantage here lies with the locals (Japanese and Chinese, and perhaps the Africans), though all the major contenders will almost certainly have spent a period of acclimatization before this race. The exact physiology behind the process is quite complex, but it involves increases in plasma volume, which enables more heat loss, increased recruitment of sweat glands, and in a race situation, the perception/sensation of heat is without doubt key as well.

The role of the brain in all this

Then finally, exercise is ultimately regulated by the brain. Whether one makes an athlete exercise in the heat until they are exhausted, or whether it is a race/self-paced situation, exercise in the heat is ultimately limited or regulated by the brain. So for example, if one runs at the SAME SPEED until exhaustion in the heat, the final body temperature is around 40 degrees. It is as if there is an 'off-switch', a point where the brain simply says enough is enough, and stops activating the muscle. And the afore-mentioned Nielsen, with Lars Nybo, have found this in studies. Once the body temperature hits this limit, the activation of muscle by the brain is reduced.

But of course, the Marathon in Osaka will not be a straight out 'run at a certain speed until you stop' affair. There are tactics and the athletes can choose to slow down or speed up depending on the race situation and their own condition and how they feel. So this 'model' of making athletes run or cycle until they simply can't anymore is a little unrealistic. Instead, one must allow exercise to be 'self-paced'. If this is done, then the really interesting thing is that the athlete slows down well before the body temperature can climb. In otherwords, the brain seems to 'anticipate' that there is a chance of overheating, and it causes the athelte to slow down by activating less muscle. The reason this is interesting is because there is no 'textbook' explanation for how it happens, and it is actually disputed. But there is some evidence, both from animals and humans, that it happens. This is certainly something that Jonathan and I (Ross) will cover in the future - we're both into the heat question.

But the point is that the athletes running the marathon will have a constant battle to run faster in the face of physiology that is telling them to slow down. Failing to slow down would cause body temperature to rise, leading to complete exhaustion, as the temperature gets closer and closer to a limit. Listening to the physiology will cause the athlete to slow down, but defend what is called thermal homeostasis. So when you are watching the athletes racing between 32 and 42 km, you're witnessing a real battle of physiology as well as between athletes. And of course, the body size and acclimatization issue are both physiology, which give an advantage to the athlete who has them both.

So enjoy the marathon, it should be a great race, tactical and relatively slow (because of the heat), but real racing.

R & J


Anonymous said...

Fabulous analysis!

I will be competing in a desert ultramarathon in a few months, and the subject of heat and performance obviously is of interest to me.

I live in a cold climate, but the race (April 2008) will have temps ranging from 25C to 45C, with low humidity.
I am hoping to acclimate by training in a heat chamber . I expect to do 5 x 100min sessions at 70% VO2max in the 10 days prior to starting the race.
Any advice as to whether this is adequate? Any better ideas?


Ross Tucker and Jonathan Dugas said...

Hi Bill, and thanks for the kudos on this post.

In fact if you subscribe via the Feedburner box, eventually we will do a series/post on heat acclimatization and exercise in the heat. Currently as the norther hemisphere winter is setting in, we will focus on exercise in the cold, but some spring we will shift to the effects of a hot environment on performance and physiology.

If you have access to a heat chamber, that is really awesome and will make an enormous impact on your preparation for the event.

Generally speaking, most of the adaptations occur within the first 7-10 days, but full acclimatization requires up to 14 days. Therefore I would recommend more frequent sessions for that period of time.

Seventy percent of VO2max is pretty intense---I suggest something more moderate especially in the beginning. It is more about the time and not about the intensity, especially in the beginning of the training. So 100 min is great, but lower the intensity else you might not finish each session.

Why don't you contact us closer to the time of your training, and perhaps by then we will have done the heat series, and if not we can provide you with some more detailed advice.

Good luck in the meantime with the distance training this winter!

Kind Regards,

Anonymous said...

Thanks Jonathan, looking forward to the heat series. Your site is a real hit amongst my medical and ultramarathon colleagues.